(1) Field of the Invention
The invention relates generally to the field of systems and methods for performing digital signal processing operations in connection with signals and more particularly to systems and methods for characterizing signals to determine their stochastic properties, that is, to determine whether they are random. More particularly, it relates to a system for performing this characterization function upon signals having embedded therein four-items of mutually orthogonal measurement information. If the signals are random, they may be determined to constitute noise. If the latter is the case then the principal function of the overall signal process (e.g., extraction of the information component) and its associated computational burden can be avoided. Stated another way, the system and method allows a determination to be made of the extent to which a pattern of data items, or sample points, representing four dimensions of measurement information conforms to a random structure of data.
(2) Description of the Prior Art
Heretofore there have been developments of systems and methods for characterizing signals representing information which is representable as a composite of two and three component items of mutually orthogonal measurement information. Illustrations of these may be found in co-pending U.S. patent applications Ser. No. 08/412,260 entitled "System and Method for Processing Signals to Determine Their Stochastic Properties" (Navy Case No. 76119) and Ser. No.08/605,292, now U.S. Pat. No. 5,703,906 entitled "System for Assessing Stochastic Properties Signals Representing Three Items of Mutually Orthogonal Measurement Information" (Navy Case No. 76836).
Some signal processing systems operate on the basis of processing four mutually orthogonal items of useful measurement information and therefor could utilize a system which makes this characterization for four mutually orthogonal data items. It is accordingly desirable to be able to determine the likelihood that a signal constitutes only noise, or whether it is likely that it also includes four mutually orthogonal items of measurement information, so that a determination can be made as to whether processing of the signal to extract the information would be useful.
Illustrative of the types of signal processing applications which process four orthogonally related items of measurement information in a noisy environment are systems for tracking distant moving objects in which accuracy of estimation of the location of the object is enhanced by the processing of three mutually orthogonal sensor-based measurements, and in which clock timing constitutes the fourth item of mutually orthogonal item of measurement information. One example of this type of system is a system for tracking the landing approach of an aircraft which is described in C. M. Rekkas, et al. "Three-Dimensional Tracking Using On-Board Measurements," IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS, Vol. 27, No. 4, pages 617-623, July 1991, hereby incorporated herein by cross-reference in its entirety.